PubMed · 14299162
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K AKISAWA. 1965. [SUDDEN DEAFNESS].. https://pubmed.ncbi.nlm.nih.gov/14299162/
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Mistuning a harmonic increases its salience and produces an exaggerated change in its pitch. The effects on component grouping of spectral pattern, global pitch, and local harmonicity were explored using these phenomena. Stimuli were either harmonic (F0 = 200 Hz) or frequency shifted by 25% of F0. Component 1 or 2 was replaced by one of a set of sinusoidal probes in the same spectral region. Listeners either matched the probe pitch by adjusting the frequency of a pure tone (experiments 1 and 3) or matched the probe loudness by adjusting the level of a tone of identical frequency (experiment 2). Probe positions corresponding to greatest perceptual fusion were estimated from the variations in pitch shift and loudness across frequency. Both measures gave similar estimates. For harmonic stimuli, fusion was greatest at harmonic values. For shifted stimuli, fusion was greatest close to the suboctave (225 Hz) and the frequency (450 Hz) of component 2. The latter value moved downwards to near 433 Hz (2:3 ratio with component 3) when component 1 was removed. Together, these results indicate that the lowest component of a shifted complex is grouped by local harmonicity, whereas the higher components are grouped by common spectral spacing. Global pitch did not influence component grouping.
Olivocochlear efferent neurons originate in the superior olivary complex of the brainstem and terminate within sensory cell regions of the organ of Corti. Components of this complex include the lateral olivocochlear bundle whose unmyelinated axons synapse with radial afferent dendrites below inner hair cells and the medial olivocochlear bundle, from which myelinated axons form a direct synaptic contact with outer hair cells. gamma-Aminobutyric acid (GABA), a major neurotransmitter of the central nervous system believed to be responsible for most fast-inhibitory transmissions, has been demonstrated with interspecies variation between mammal and primate auditory efferents. In the present study, we evaluate the immunocytochemical presence of GABA in 10 human cochleae using light and electron microscopy. GABA-like immunostaining could be observed in inner spiral fibers, tunnel spiral fibers, tunnel-crossing fibers, and at efferent endings synapsing with outer hair cells. To approximate medial efferent fiber quantifications, we counted labeled terminals at the base of each outer hair cell and then compared this sum with the number of tunnel crossing fibers. We found a 'branching ratio' of 1:2 implicating a doubling in quantifiable efferent fibers at the level of the outer hair cell. In human, the distribution of GABA-like immunoreactivity showed a consistent presence throughout all turns of the cochlea. A new method for application of immunoelectron microscopy on human cochleae using a pre-embedding technique is also presented and discussed.